(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Three identical point charges, each of mass 80 g and charge +q, hang from three strings,

as in the figure.

The acceleration of gravity is 9.8 m/s2,

and the Coulomb constant is 8.98755 × 109 N · m2/C2.

If the lengths of the left and right strings

are each 11.1 cm, and each forms an angle of

47◦ with the vertical, determine the value of

q. Answer in units of μC.

2. Relevant equations

W = mg

F = (kq^{2}) / r^{2}

SOHCAHTOA

3. The attempt at a solution

It seemed to be a relatively easy problem, but I just keep getting it wrroooong.

So in the x-direction..

mg tan (theta) = [ (kq^{2}) / L^{2}sin^{2}(theta) ] + [ (kq^{2}) / (4L^{2}sin^{2}) (theta)) ]

sqrt [ (mg * tan (theta) * 4L^{2}sin^{2}) (theta)) / (5k) ] = q

q = 7.02271226 x 10^{-13}C

q * (10^{-6}) = 7.02271226 x 10^{-13}micro C

Which iswrong.

EDIT: OH GOD!!!! I multiplied times 10^-6 instead of 10^6. Can someone at least check if my process is right though?

FOR CLARIFICATION:

x-component of weight on left mass: mg tan theta

length of string: L

x-length from vertical to left mass: L^{2}sin^{2}(theta)

x-length from right mass to left mass: 2*L^{2}sin^{2}(theta)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: 2D Electrical force problem

**Physics Forums | Science Articles, Homework Help, Discussion**